1. Field of the Invention
The present invention relates to a method of controlling a motorized window treatment, and more specifically, a method of controlling a motorized roller shade during a motor overload or low-line condition.
2. Description of the Related Art
Motorized window treatments typically include a flexible fabric or other means for covering a window in order to block or limit the daylight entering a space and to provide privacy. The motorized window treatments may comprise, for example, roller shades, Roman shades, or draperies. The motorized window treatments include a motor drive for movement of the fabric in front of the window to control the amount of the window that is covered by the fabric. For example, a typical motorized roller shade includes a flexible shade fabric wound onto an elongated roller tube with an electronic drive unit installed in the roller tube. The electronic drive unit includes a motor, such as a direct-current (DC) motor, which is operable to rotate the roller tube upon being energized by a DC voltage.
In order to provide for advanced control of the roller shade, the electronic drive unit comprises a microprocessor or other processing means. The microprocessor is operable to control the rotational speed of the roller tube, to store a fully open position (i.e., an open shade limit) and a fully closed position (i.e., a closed shade limit), and to recall a preset position of the shade fabric. The microprocessor keeps track of the position of the shade fabric by counting the rotations of the motor shaft and determines when the shade fabric has moved to a desired position. The microprocessor receives power from a DC voltage supplied by an internal power supply in the electronic drive unit.
Motor overload conditions and low-line conditions may cause the DC voltage of the internal power supply of the electronic drive unit to drop below the voltage level required by the microprocessor to remain operational, and thus, may cause the microprocessor to reset. For example, the motor may suddenly draw a large amount of current if the electronic drive unit is driving the motor, but the shade fabric is unexpectedly prevented from moving. A transitory large current drawn from the power supply of the electronic drive unit may cause the DC voltage to drop below the regulated level and thus cause the microprocessor to reset. As used herein, an overload condition of a motor is defined as an event that causes the motor to suddenly draw a much larger amount of current. A motor may draw, for example, approximately 800 mA to 1.5 A during normal operation, and approximately 2 A to 10 A during an overload condition.
Further, if the voltage received by the internal power supply drops below the required input voltage of the power supply (i.e., the drop-out voltage), the DC voltage supplied by the internal power supply may drop below the regulated level.
If the microprocessor resets during movement of the roller shade, the position information maintained by the microprocessor may become inaccurate, which could also prevent the microprocessor from moving the shade fabric. Thus, there is a need for a method of controlling a motorized window treatment, in which the microprocessor is operable to control the motorized window treatment without resetting in the occurrence of an overload condition or a low-line condition.